1. Field of the Invention
The present invention relates to a thin-film magnetic head layer structure including two magnetic shanks. More particularly, the invention relates to a unique combination configuration for the two magnetic shanks whereby a reading pole including one of the magnetic shanks reads an area narrower than an area written by a writing pole of the other magnetic shank.
2. Related Art
A thin-film magnetic head is to be guided over a data track of a magnetizable recording medium. The head employs one of the known principles of storing data on a recording medium.
The principles of storing data on a recording medium, such as a disk-shaped medium, using longitudinal (horizontal) magnetization or perpendicular (vertical) magnetization are generally known as disclosed in "Perpendicular Magnetic Recording", IEEE Transactions on Magnetics, Vol. MAG-16, No. 1, January 1980, pages 71 to 76 or "Perpendicular Magnetic Recording - Evolution and Future", IEEE Transactions on Magnetics, Vol. MAG-20, No. 5, September 1984, pages 657 to 662 and "Perpendicular Magnetic Recording - Its Basics and Potential for the Future" appearing in the same publication at pages 675 to 680. A magnetic head utilizing one of these principles may contain a magnetic ring core head type guide body that carries a magnetic flux with a first and a second magnetic shank. These magnetic shanks may each have at least one magnetic layer with a predetermined magnetic response behavior. Also, the shanks may form magnetic poles facing the recording medium, which poles are arranged sequentially with respect to a relative direction of motion of the magnetic head with respect to the recording medium. The poles are separated by a predetermined gap width and have predetermined width that is transverse to the relative direction of motion. The magnetic shanks also form the boundary of an intermediate area outside the pole region through which the windings of a write and/or read coil Winding extend.
A corresponding magnetic head can be found, for example in European Patent Application EP-A-O 232 505 corresponding to U.S. Pat. No. 4,742,413 assigned to the Assignee of the present application. This magnetic head writes with a quasi-single pole head using only a single magnetic shank operating by vertical magnetization. To this end, the two magnetic shanks are so formed that they show different magnetic responses during the write function rendering only one of the poles effective. The read function, in contrast, is carried out with both magnetic shanks.
Manufacturing technology for known magnetic heads for longitudinal magnetization with stepwise structure of the layers of their individual magnetic shanks and with a subsequent microstructuring can produce a first magnetic shank deposited first on a non-magnetic substrate. In the region of a magnetic pole of the first shank, the shank has a somewhat greater width that is transverse to the relative direction of motion of the head with respect to the recording medium than the magnetic pole of the later deposited second magnetic shank. If, however, writing takes place with such a longitudinal magnetic head, it becomes apparent that in this process the width of the magnetic pole of the second magnetic shank, which is narrower than the magnetic pole of the first shank, is predominantly effective. In reading, however, the magnetic margin fields effect a flattened decrease of the read field profile toward the margin between the two magnetic poles. Therefore, it is possible to speak of concomitant reading of the right and left margin regions of the track by the margins of the broader magnetic pole, i.e. of the margin of the broader magnetic pole of the first magnetic shank that extends laterally beyond the narrower magnetic pole of the second magnetic shank.
In data storage systems with high data densities that use the vertical magnetization principle, track guidance systems are required to ensure guidance of the corresponding magnetic heads over the data tracks with a high track locking accuracy "sf" of, for example, less than .+-.0.5 .mu.m. Corresponding track guidance systems are known, for example, as "Dedicated Servo Systems". However, the writing of neighboring tracks to be carried out with corresponding tolerances must be taken into consideration. The result is a track guidance error greater than the mentioned .+-.0.5 .mu.m. If the mentioned magnetization conditions in known longitudinally magnetizing magnetic heads having different widths of their magnetic poles are taken as the basis, then a track guidance error of the mentioned Dedicated Servo Systems of the indicated order and magnitude consequently leads to the fact that after repeated overwriting of a data track the lateral margins of the data tracks loose sharpness They become "frayed." In an extreme case the gap region between neighboring data tracks, frequently referred to as a "lawn" which may be 3 to 4 .mu.m wide for example, is at least in some locations completely written over. This means that in the margin region of the data tracks insular data residues of different overwrite processes can remain. When reading these tracks read errors may occur due to the ability of the margin regions of the broader magnetic pole of the first magnetic shank to read the margin regions of the track.
Due to this difficulty combined magnetic heads have been developed which in writing inductively lay down a broad traCk and in reading using an integrated narrower magnetoresistive sensor to read a track with a width narrower than that for writing. Such heads are disclosed in an article entitled "A NEW TYPE OF MAGNETIC HEAD MAY BE JUST AROUND THE CORNER" in Electronics, May 14, 1987, pages 31 and 32. The expenditures required for the manufacture of these highly complex heads are considerable. In addition, the sensitivity of magnetoresistive heads to magnetic spreading or strewing, which is well known, can lead to problems.